UV Sterilizer with GTL3 bulbs

Discussion in 'The Projects Forum' started by sderrick, Jul 22, 2012.

  1. sderrick

    Thread Starter New Member

    Jul 22, 2012
    5
    1
    I'm getting ready to order parts to build a UV water sterilizer using the GTL3 UV bulb.

    http://www.lightbulbsurplus.com/index.php?main_page=product_info&products_id=327

    It looks like an incandescent but I'm not sure, I know it has mercury in it aka mercury vapor? I'm wondering if it needs a higher starting voltage? I was going to use a DC-DC linear regulator like this one, I have ample 24-30 vdc supply from a solar setup.

    http://www.acopian.com/store/dcdc-narrow-t.aspx?min=18&max=36

    There will be about 20 GTL3's in parallel to generate 60 watts of UV.

    Can I just hook um up in parallel and throw the switch?

    thanks,

    Scott
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC!

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  3. #12

    Expert

    Nov 30, 2010
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    That looks like a 3W, 10.5V, incandescent bulb. .286 amps each. The presence of filaments suggests that it just needs 10.5 volts. Total = 5.71 amps except that incandescent lamps have a cold start surge current that is rather high and might put a high tech supply into self-protect mode.

    It looks like you are skimping with a 5 amp supply module, and at $185 each, this is why people like us make our own power supplies!

    Your response?
     
  4. sderrick

    Thread Starter New Member

    Jul 22, 2012
    5
    1
    I know it "looks" like an incandescent bulb, but I think its a Low-Pressure Mercury-Arc lamp,
    which is my concern.

    Do I have to do anything special with starting voltages or can I treat it like any other incandescent bulb and just hook up the power and it will self regulate?

    I found this conversation http://forum.allaboutcircuits.com/showthread.php?t=68736 but its inconclusive.

    From the above conversation it looks like I need to limit the current through the bulb by using a series resistor and a cap to help it start?

    And thanks for the heads up on the power supply, I can easily get the next larger model.

    Scott
     
  5. #12

    Expert

    Nov 30, 2010
    18,082
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    Last edited: Jul 23, 2012
  6. sderrick

    Thread Starter New Member

    Jul 22, 2012
    5
    1
    No that's not right. Those ballast's are for much larger wattage and AC voltage. This is a 10.5 dc 0.3 watt light bulb.

    There seems to be much confusion on the light bulb sites about ballasts and these bulbs. Some say no ballast required others say they are required but don't know which one? Of course most light bulb sites don;t know squat about what they are selling, they just sell stuff.

    Scott
     
  7. bertus

    Administrator

    Apr 5, 2008
    18,682
    3,633
    Hello,

    I do not know the lamps, but I could imagine that the filament is heating the mercury to have the UV portion of light.

    Bertus
     
  8. takao21203

    AAC Fanatic!

    Apr 28, 2012
    3,783
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    No joke or hoax product. Regular product.

    The filaments are not the high temperature type. Looks similar to CFL filaments (or 4W tube).

    You won't get UV if you just power the filament. This is what I guess.
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    The description of the GTL3 states:
     
  10. #12

    Expert

    Nov 30, 2010
    18,082
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    Takao: Again I ask, where does the arc current travel considering there are only 2 contacts on the lamp?

    Answer: It doesn't.

    as djsfantasi just pointed out, these are INCANDESCENT lamps.

    The ballasts I pointed out are sold on the same site, to power UV bulbs, but they are for T5 tubes. After searching diligently, that site does not sell a "ballast" or "fixture" for those bulbs. I can only come to the conclusion that they are 10.5 volt incandescent bulbs and they need 10.5 volts AC RMS or DC.
     
  11. sderrick

    Thread Starter New Member

    Jul 22, 2012
    5
    1
    I think they are as published, Low Power Mercury-Arc lamp bulbs.

    However as somebody previously mentioned they use the filament to provide the heat/arc. Once the filament heats up enough the mercury is lit off and voila, UV light in the 253 nm range!

    The key is to use a current limiting supply or run the bulb in series with a resistor. I'm going for the supply, have ordered one and a few bulbs.

    I'll report back my results.
     
    #12 likes this.
  12. takao21203

    AAC Fanatic!

    Apr 28, 2012
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    We should apply reason here for this device.

    The filament to me clearly does not look like high temp. incandescent.

    Maybe a special fixture is used, with an external foil pad that works through the glass? And so, maybe needs a special ballast.

    Not so special to me, a small CCFL inverter etc. might work well.

    I also don't get why you put efforts into it. 4W etc. regular UV tubes are cheap.
     
  13. takao21203

    AAC Fanatic!

    Apr 28, 2012
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    Most gas discharge devices I am aware of use inductive ballast.

    How can the gas discharge happen? 10V between the two heated filaments? That looks a little low to me.

    I rather guess a special fixture is used for these, using for instance a foil pad.

    When I connect one wire from CCFL inverter to a CFL tube, and touch the glass with my hand, the CFL lights up.
     
  14. sderrick

    Thread Starter New Member

    Jul 22, 2012
    5
    1
    All guesses. It's nice to wonder how something works, but in the end, facts are whats needed.

    I can only assume nobody who's read this thread really knows how a DC Low Power Mercury-Arc lamp works. Everybody is basing there "guesses" on how high voltage AC fluorescent and arc lamps lamps work.

    It like having only ever seen an incandescent and trying to describe an LED light.

    Scott
     
  15. takao21203

    AAC Fanatic!

    Apr 28, 2012
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    I know how 4 Watt UV tubes work. Including I have used them myself, with different kinds of inverter circuits.

    However this small bulb is not very common. It is not very likely that many replies can exist of a person who is using these bulbs, has used them, or knows them at all.

    Why not use a regular UV tube? These bulbs seem to be speciality product.

    I have at least looked up the manufacturer website.

    If I have professional requirement to use the bulbs, I would contact them.
     
  16. Yamato71

    New Member

    Dec 21, 2017
    3
    3
    The GTL3 is indeed a mercury vapor discharge lamp, one with an ingenious design. For the first second or so, the lamp behaves like any other incandescent bulb. Applying 10.5 volts, AC or DC heats the filament, which in turn heats the mercury vapor in the vicinity of the filament structure. As we learned in high school physics, matter that is hot exhibits a large vibrational moment compared to matter that is cooler. This is known as Brownian motion and all matter in the universe that is warmer than absolute zero exhibits this phenomenon.

    Any random mercury atom in the vacuum envelope that happens to drift into the hot filament will suddenly absorb a relatively large amount of thermal energy, causing it to rocket away from the filament with high velocity until it strikes something in the bulb. The lamp designers are counting on that high speed mercury atom to strike another mercury atom. When this collision occurs, one or more of the loosely held electrons in the two colliding atoms are literally knocked out of orbit. One or more of the mercury atoms is now ionized, having taken on a positive charge. This by the way is the same process that charges thunderstorms and produces lightning, except with ice crystals colliding instead of mercury atoms. If you slowly raise the voltage to the bulb, you can actually see the mercury vapor near the filament glowing a pale blue color.

    While the heated filament is ionizing mercury vapor and argon near the filament, another phenomenon is occurring that will cause an arc to strike through the mercury vapor. As is evidenced by the comments above, it is counter intuitive that an appreciable electric current can be made to flow through the Hg vapor since there is no apparent return path for the arc current.

    QUESTION: How does the arc lamp pass current through a single ended circuit (the path through the mercury vapor)?
    ANSWER: It doesn't

    Another high school physics factoid is that a hot metal wire is is less conductive (more resistive) than an identical piece of wire at a lower temperature. At room temperature, the filament of the GTL-3 lamp is nearly a short circuit and draws a large inrush current. Less than a second after current is turned on, the tungsten filament is glowing red hot and its resistance has increased considerably, causing the current flowing through it to decrease by the same amount. If you were to look at the voltage across the filament and record its value over the interval between the moment that voltage was applied (T0) until the filament reached operating temperature (T1), you would observe something interesting. At T0, the filament is cold, almost a dead short. The voltage across the filament would very low, nearly zero. As the filament heats up, the filament resistance will increase, decreasing the current through it but increasing the voltage across it. Some of you noticed the unusual geometry of the filament, It's long, to maximize the effect of temperature on the filament current, but the two ends of the filament are situated very close to each other. The voltage across the filament eventually rises to the 10.5 volt supply voltage, which happens to be a high enough voltage to sustain a short arc between the two ends of the filament. Since the mercury vapor around the filament has already ionized due to the thermal effects discussed earlier, the current from the power supply begins flowing through the ionized vapor in the short gap between the ends of the filament. From this point, most of the supply current is passing through the mercury vapor, bypassing the filament. The arc discharge plays along the filament, heating it to incandescence, keeping its resistance very high. Unless a ballast resistance or current regulation is employed in the power supply, the negative resistance curve of the arc will cause it to draw increasing current until the lamp is destroyed. Also, lamp life is lengthened considerably by powering it with AC instead of DC. The cathode of the any discharge lamp bears the brunt of wear and tear. Having both ends constantly changing polarity forces the electrodes to evenly share the load.
     
    groundeffect and RichardO like this.
  17. RichardO

    Late Member

    May 4, 2013
    2,274
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    Thanks for all of the information. :D:D

    I have an old UV lamp I use for exposing UV sensitive PCB's. It was originally sold for some kind of light therapy -- maybe for skin.

    It has a standard 120 volt Edison base. Other than running on 120 volts, its operation sounds very much like what you describe.

    When I get a chance, I will get the number off the lamp and post it here for reference.
     
  18. Ylli

    Member

    Nov 13, 2015
    401
    103
    Interesting article here:
    http://russellsrandomthoughts.blogspot.com/2013/05/the-gtl3-bulb-simple-and-inexpensive.html

    And Don Klipstein says this:
    "
    Apparently Incandescent Ozone Lamps
    These look like incandescent bulbs. These bulbs are roughly of ping pong ball size, about 1-3/8 inch (about 35 mm.) in diameter. They have an intermediate screw base, or sometimes a bayonet base like that of an auto taillight bulb. The filament is roughly V-shaped or a sharpish U-shape, with one support at the tip. These bulbs are sometimes labeled "Puritron" or "Odorout" and may also be labeled "protect eyes" and also "4 watts". In the past, these bulbs were used in some dryers to kill germs and oxidize odors.
    In these bulbs, an arc forms across the ends of the filament. These bulbs need a current-limited (or high resistance) power supply that delivers about .33 to .4 amp to the bulb with about 10.5-12 volts across the bulb. Do not connect these bulbs to voltage-regulated power supplies; either little/no arc will form or the arc will "blow up" and melt one or both ends of the filament."

    http://donklipstein.com/uvbulb.html
     
    Last edited: Dec 22, 2017
  19. RichardO

    Late Member

    May 4, 2013
    2,274
    890
    What I have is a sunlamp.

    GE Sunlamp Order code -- RS. CG401-E16RS is on lid flap. The lamp is marked "66". It is floodlight shaped and about 5" in diameter. It's rated at 275 watts.

    From the box:
    "This lamp warms up slowly. After being turned on, this sunlamp will flicker and gradually change color. Normal ultraviolet output output is reached in 3-5 minutes."
    "If turned off, this lamp cannot be re-started immediately. Aftyer this lamp has been turned off, the starting mechanism will not function until it has cooled down. Several minutes' cooling are usually required before the lamp can be started again."
     
  20. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,617
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    There is more to this than is immediately apparent. This site: https://www.alibaba.com/product-det...ml?spm=a2700.7724857.main07.71.3eb8b3a4JUftuF describes it as "self-ballasted". Look at the picture; there are a couple of white cylindrical things in series with the filament. I think that 120 VAC is applied, warms up the filament which then emits enough electrons to start the arc across the 120 volt ends of the filament. The white things limit the current to the arc.

    This picture: https://www.ebay.com/itm/Replacemen...248215&hash=item4aca88c56e:g:XxYAAOxyHntSVhdd

    also shows the white things.

    However, check out the schematic about halfway down the page here:
    https://www.alibaba.com/product-det...ml?spm=a2700.7724857.main07.63.3eb8b3a4JUftuF

    I wouldn't think that 12 volts would be enough to strike the arc. Perhaps the "12 VDC inverter" shown can produce a high voltage to start the arc before supplying the 12 volts running voltage. But the capacitor in series method is fairly obvious.
     
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